1. Field of the invention
The present invention concerns a dynamometer link, that is to say a link adapted to provide information relating to the magnitude of forces that it transmits along a longitudinal axis.
2. Description of the prior art
French patent 2 434 377 discloses a link of this kind comprising at least two male and female members disposed to slide axially one within the other and spring-loaded by respective spring means so that a force transmitted by the link causes a relative displacement representing said force. This relative movement is detected by a lever pivoting inside the female member one end of which cooperates with a cam carried by the male member and the other end of which is adapted to operate a microswitch when the relative displacement of the two members and therefore the pivoting of the lever exceeds a particular threshold.
Of course, to avoid any disturbance of the kinematic system in which the link is incorporated, the relative displacement of the two members must be as small as possible and must preferably lie outside the range of normal loads on the link.
To this end the prior art patent provides for:
prestressing the spring means so that relative displacement of the two members occurs only beyond a predetermined force threshold; PA0 dimensioning the lever and disposing the microswitch so that the latter is operated only beyond a second force threshold higher than the first.
The solutions put forward in this prior art patent have two drawbacks.
The first is that the cam-abutment-lever system is relatively bulky and requires relatively high amplification of the relative movement detected and consequently a long lever. The female member of the link which contains this system must therefore be relatively long and bulky. The use of two levers, one of which carries the microswitch, makes it possible to reduce the length of this member by half. However, this reduction in the length is achieved at the cost of an increase in the diameter.
The second drawback is that this device cannot determine the direction of the force transmitted by the link. This information is relatively important because it makes it possible to distinguish a driving force from a force due to an external force applied to the load.
A particular object of the invention is to eliminate these drawbacks.